Currently known battery powered key entry devices may be classified into two general groups.
The first group comprises calculators, extending from the simplest four function type through to the considerably more powerful programmable calculators as exemplified by the 600 and 700 series of calculators produced by Casio Corporation. All of these devices are not normally used continuously for any great length of time. The usual operational method is to switch the device on, perform one or more calculations, and then switch off. With such operations, and depending on the form of display employed, the batteries in calculators last from several months to years. In order to conserve the batteries in the event that a calculator is left on after operation, many such devices employ an arrangement in which, some minutes after a key operation, the microprocessor is switched to a standby-mode, and the display is switched off. Thereafter, the microprocessor and display are powered up by depression of a particular key, normally the CLEAR key.
The second group comprises remote control devices, for example television remote control units. In operation, these consume much more power than the average calculator as they employ some form of transmission device, such as an infra-red generator. Such control devices are normally used relatively infrequently and for short periods. Typically, a television remote control unit may generate a sequence of up to about ten control pulses during each of up to ten to twenty times a day. Between operations, these units are switched off completely. Consequently, battery drain offers no significant problem.
If, however, it is required to provide a remote self-contained, battery powered keyboard entry device for, for example, a microcomputer, battery life becomes a significant problem. Such a device may be in substantially continuous use throughout each day of a working week. With such operational conditions, without some form of battery conservation system, battery life may prove insufficient to ensure reliable operation without frequent battery changes.
It is, therefore, an object of the present invention to provide a power conservation system in such a keyboard entry device.